High-frequency heating



Patented Aug. 10, 1954 HIGH-FREQUENCY HEATING Theodore P. Kinn,

Baltimore, Edward M. Wharfl,

Jr., Ellicott City, and Milton P. Vore, Catonsville, Md., assignors toWestinghouse Electric Corporation, East P tion of Pennsylvaniaittsburgh, Pa., a corpora- Application August 12, 1950, Serial No.179,072

9 Claims. 1

Our invention relates to high-frequency heating systems, and moreparticularly to high-frequency heating systems of a type having aplurality of work-treating stations, each including a high-frequencywork-heater, the stations being energized from a single source ofhigh-frequency in a sequence which can be repeated indefinitely.

It is recognized that a high-frequency source of power, such as atube-oscillator generator, can be more economically employed when itsduty cycle, that is the ratio of its active work time to its idle time,is as high as possible. When a plu rality of work-treating stations areto be alternating or sequentially energized by the same generator,certain problems arise because of the high frequency and the highcurrents involved. Difficulties that may be encountered are set forth inDravneek Patent No. 2,321,189, dated June 8, 1943 and in Zottu PatentNo. 2,419,307, dated August 22, 1947.

These patents, representative of the prior art, show systems forselectively energizing a plurality of work-treating stations by means ofa circuit selecting means involving a transfer switch which selectivelyconnects the high-frequency generator to whatever work-treating stationis to be energized, the remaining work-treating stations beingdisconnected and deenergized during such connection. As onework-treating station is energized, the other or others are unloaded andre" loaded. The energized work-treating station is then deenergized byoperation of the transfer switch, and the high-frequency generatorconnected to a second work-treating station. In this manner a system ofhigh capacity is provided which can economically utilize ahigh-frequency generator of comparatively small rating because most ofthe energy which the generator is called upon to supply is that demandedby a single work-heating station. However, the use of a switching meansrequires engageable and disengageable contacts, so that a complicatedswitching mechanism must be used because it is necessary to transferhigh-frequency currents and voltages from a circuit including a firstwork-treating station to a different circuit including anotherwork-treating station.

An object of our invention is to provide a system in which ahigh-frequency generator can be sequentially effective on a plurality ofwork-treating stations without the use of transfer switching meanshaving make-and-break contacts.

A further object of our invention is to provide an induction heatingsystem in which a single high-frequency generator and a plurality ofhighfrequency worktreating stations are connected in a single circuitthat has no transfer switching means; the system nevertheless includingmeans which permits the energy to be selectively supplied from thegenerator to any grouping of work-treating stations, less than all ofthem.

An ancilliary object of our invention is to provide a system of the typedescribed in which a single high-frequency tube-oscillator source ofpower is connected selectively to each of a plurality of work-treatingstations through a single circuit which is not altered while thedifferent work-treating stations are selectively operated.

A further object of our invention is to provide a system of the typedescribed in which a single tube-oscillator generator selectivelyenergizes each of a plurality of induction-heating coils connected in asingle circuit; the selective operation being such as to maintain theelectrical characteristics of the load presented to the highfrequencytube-oscillator generator substantially constant. v

An over-all object of our invention is to provide a high-frequencyheating system of the type described in which the tube-oscillatorgenerator may be operated as nearly continuously as possible.

The principles of our invention are of broad application but are hereindescribed in connection with preferred forms thereof, having a pluralityof high-frequency work-treating stations, each of which includes awork-heater in the form of an induction-heating coil. The work-treatingstations are connected in a common circuit that has no transferswitching means such a used in the prior art. Each work-treating stationalso includes work-holder means which holds work that is to be heated bythe associated induction-heating coil.

When the induction-heating coils are selectively operable, those whichare not supplied Wtih work are instead supplied with a piece of metal,in the form of a coil or block or other similar form; the metal being ofhigh conductivity such as copper or silver, for example. The piece orpieces of metal are closely coupled to the nonworking induction-heatingcoils. Physically, each piece of metal is as near as practical to theassociated coil without touching it or introducing the danger ofpark-over. The close coupling and high conductivity of the metal-piecespractically nullifies the inductance of the non-workinginduction-heating coils without the absorption of a great deal of power.

Objects, features and innovations of our in- 3 vention, in addition tothe foregoing, will be discernible from the following description ofpreferred embodiments thereof, to which our invention is obviously notlimited. The description is to be taken in conjunction with theaccompanying drawings. Both the description and drawings are highlysimplified for clearly setting forth the principles of our invention,without the use of excessive detail. In the drawings:

Figure 1 is a sectional view substantially on the line 1-1 of Figure 2;

Fig. 2 is a vertical view, partly in section and partly in elevation, ofa high-frequency heating system embodying the principles of ourinvention;

Fig. 3 is a vertical view, partly in section and partly in elevation, ofa modified part for a system such as shown in Figs. 1 and 2; and

Fig. 4 is a schematic wiring diagram of a further modification for asystem embodying the principles of our invention.

A high-frequency tube oscillator generator unit is represented in Fig. 1by the reference numeral 2. As is known to the art, such a unit usuallycomprises a housing which contains suitable electronic tubes, circuits,transformers and further equipment for the generation and over-allcontrol of high-frequency energy which is delivered to a pair ofconnectors or terminals 4 and 6 carried by a shelf 8 on the outside ofthe unit. Secured to the terminals 4 and 6 are a pair of highfrequencypower-supply conductors Ill and [2 to which a plurality of Work-treatingstations are connected. Two such stations I4 and [6 are indicated in thepreferred embodiment, each comprising as many work-receivinginduction-heating coil-units or openings as desired. The coils of eachwork-heating station are similar and may be either individual coils or aunit equivalent to several coils, as is known to the art.

In the present embodiment being described, the induction-heating coil ateach work-heating station is constructed as a unit by providing in awell-known manner, work-receiving holes or cut-out portions I8 and 20 ina plate 22 for the work-treating station l4, and work-receiving holes orcut-out portions 24 and 26 in a plate 28 for the work-treating station16. As is customary in such constructions, slots 30 are provided betweenthe cut-out portions and a single end of the associated plate so that inefiect each work-treating station comprises two work-receivinginduction-heating coil-parts connected in series. Preferably the platesare made of copper orother highly conductive material.

For convenience and to allow a single operator to supervise bothwork-treating stations, the induction-heating coil-unit 22 is endwisealongside the induction heating coil-unit l6, and both are connected inseries to the power supply conductors l and I2. For such connection, theslotted ends of the coil-units 22 and 28 are edgewise adjacent, and thepower supply conductors l0 and I2 are electrically intimately connectedto one side of facing end portions thereof, respectively. The otherfacing side portions of the plates are electrically intimately connectedby a jumper conductor 32 in the form of a small copper plate.Consequently, the coil-units 22 and 28 are connected in a series circuitwhich passes directly, without interruption, from and between the twoterminals 4 and 6.

In accordance with our invention, the induction-heating coil-units 22and 28 are alternately repeatedly operated for'heat-treating worktherein, without the use of make-and-break transfer switches. To thisend, our system comprises a power-selecting means, or power-selector,which is external to the induction-heating coils and the power supplyconductors, and is in no way mechanically connected thereto.

7 The power-selecting means is in the nature of a power-transfer meansrather than a circuittransfer switch, and preferably has as manypower-transfer means as there are work-treating stations, and as manypower-transfer devices as there are work-receiving holes. Eachpowertransfer device comprises a metal coil or block, or the equivalent,made of a metal of high conductivity, such as copper or silver. Eachpowertransfer device is arranged to move between a position inside ofthe associated work-receiving hole that is in inductive relationtherewith, and a position outside thereof that is out of inductiverelation therewith. More specifically, the powerselecting means isindicated in its entirety by the reference numeral 42, and comprises. aplurality of power-transfer means 44 and 46 respectively associated withthe work-treating stations 14 and I6. The power-transfer means 44comprises power-transfer devices 48 and 50 associated with theinduction-heating coil-unit 22; and the power-transfer means 46comprises power-transfer devices 52 and 54 associated with theinduction-heating coil-unit 28. The power-transfer devices 48, 50, 52and 54 are shown for simplicity as having the shape of solid cylinders,each of which closely fits into a work-receiving hole of aninduction-heating coil without contacting the walls defining such holes.More specifically, the

power-transfer devices 48, 50, 52 and 54 are associated respectivelywith the cutout portions 18, 26, 24 and 26 of the induction-heatingcoil-units 22 and 28 of the work-treating stations I4 andl6.

The power-selecting means 42 also comprises a plurality of reciprocableplates or supports 56 and 58 that are movable on fixed vertical guiderods 60 and 62 respectively. The plate 56 is associated with thepower-transfer means 44, and has secured thereto depending supports orrods 64 for the power-transfer devices 48 and 50; and the plate 53 isassociated with the power-transfer means 46 and has secured theretodepending supports or rods 66 for the power-transfer devices 52 and 54.

Each work-treating station also comprises one or more work-holdersadapted to place work to be heat-treated in the associatedinduction-heating coil. As represented in Fig. 2, the work-treatingstations l4 and I6 are provided with workholders 6B and 16,respectively, below the induce: tion-heating coil-units 22 and 28,respectivelyponthe side of the last which is opposite to the side atwhich the power-transfer devices are located. The work-holders 68 and 10comprise work-supporting plates 12 and 74, respectively; eachworksupporting plate having means for receiving;-

work-receiving adapters corresponding to the number of work-heatingholes at the associated;-

work-treating station- As shown in Fig. 2 the support-plates l2 and 14removably receive workreceiving adapters l6 and I8, respectively.- Eachadapter comprises a seat for receiving a piece of work W and a centralwork-centering stem 80. This centering piece extends a significantdistanceabove any work that might be placed on the ass sociated adapter.q

The work-treating stations [4 and It also comprise work-reciprocatingmeans 82 and 84: for operating the work-holders 68 and 16, respectlvely.The reciprocating means 82 and 84 comprise reciprocable piston rods 86and 88, respectively, operable in suitable pneumatic cylinders. Thesecylinders ar controlled either manually or automatically through anysuitable controls represented by valves 94 and 86 for work-holders 68and 10, respectively.

In the operation of the equipment thus far described, it may be assumedthat the equipment is in the position shown in Fig. 2 where thework-treating station I6 is in the condition having its work-holder 10loaded with ferrous or iron work-pieces W and its reciprocating means 84holding the work-holder raised so that the work W is in the holes 26 and24 of the induction-heating coil-unit 28; and where the worktreatingstation I4 has its work-holder 68 and reciprocating means 82 in lowerposition where work can be loaded on its adapters I8.

In such condition, it is to be observed that at the work-treatingstation I 6, the centering stems 80 of the work-holder I0 has raised thepowertransfer devices 52 and 54 to a position well above theinduction-heating coil-unit 28 of the associated work-treating stationI6. In this position, the power-transfer devices are, for practicalpurposes, out of inductive relation with the induction heatingcoil-unit.

At the other work-treating station I4 the power-transfer devices 48 and50 fall, by gravity, into a position in which they are fully immersed inthe magnetic fields of the holes I8 and 0f the induction-heatingcoil-unit 22 of the worktreating station I4. Th highly conductivedevices" 48 and 50 are in full inductive relation with the coil-unit 22,and the inductance of the coilunit is materially decreased with closedcoupling between the devices and the coil unit.

If now the high-frequency tube oscillator generator 2 is energized tosupply high-frequency energy to th power-supply conductors I0 and I2,current will new in a. single complete circuit, starting at a terminal 4and passing successively through the power-supply conductor I0, alongthe coil-unit or plate 22 of the work-treating station I4, across theconnection plate 32, along the coil-unit or plate 28 of the worktreatingstation I6, to the power-supply conductor I2, and to the other terminal8. The inductance of this circuit is determined by the inductance of theconductors I0, I2 and 32 which remains unchanged, and the inductance ofthe two coil-units 22 and 28. These two coil-units are alike except forthe material in their work-receiving holes. This material comprises thework-pieces W in the holes 22 and 24' of the coil-unit 28, and thepower-transfer devices 48 and 50 in the holes I8 and 20 of the coil-unit22.

Assume now that th work-pieces at the worktreating station I8 have beenheated. The power to the generator 2 may be cut oil and the workpiecesmay b quenched if desired, by means not shown. The reciprocating means82 and 84 are operated so that the position of the work-holders 68 and10 are reversed, that is the work-holder I0 is lowered and thework-holder 68 is raised. When the work-holder 10 of the work-treatingstation I6 has dropped fully, the treated work can be removed therefrom,and new work placed thereon.

In dropping, the work-holder 10 permits the power-transfer devices 52and 54 of the powertransfer means 46 to drop into the holes 26 and e 24of the induction-heating coil-unit 28.

f The work carried by the work-holder 68 of the 6 work-treating stationI4 is now in the work-receiving holes I8 and 20 of the coil 22, anddevices 48 and 50 of the power-transfer means 44 are raised to positionsout of inductive relation with the coil-unit 22.

Accordingly, the conditions of the work-heating stations I4 and I6 arereversed from that shown in Fig. 2; and work in the work-treatingstation I4 can be heated while treated work at the work-treating stationI6 is being removed and new work placed therein.

It is to be observed that the over-all inductance of theinduction-heating coil-units 22 and 28 in the single circuit is notmaterially altered when the conditions of the two work-treating stationsI4 and I6 are reversed, since electrically the inductances of thecoil-units 22 and 28 have merely been transposed. Hence, thepower-selecting means 42 operates to transfer power between thecoil-units 22 and 28 by alternate operation of the power-transfer means44 and 46 associated, respectively, with the coil-units 22 and 28.

In the embodiment shown in Figs. 1 and 2, the power-transfer means 44and 46 of the powerselecting means 42 are alternately or sequentiallyoperated by the single pair of reciprocating means 82 and 84. However,it is clear that any suitable means can be used to place and remove workfrom the respective induction heating coil-units and in oppositesequence to remove and place the power-transfer devices of thepower-transfer means 44 and 46 in the same coil-units.

Fig. 3 illustrates an embodiment in which a separate pneumaticreciprocating means controlled by a valve 92 operates to raise and lowerpower transfer devices 95 and 9! into and out of a cooperating inductionheating coil. To this end, the reciprocating means 90 is in the form ofa cylinder that operates piston rod 98 connected to the support plateI00 from which the powertransfer devices 95 and 9'! are dependinglycarried, in a manner similar to that described in connection with thepower-transfer means of Fig. 1.

Any suitable means may be used to control the power supply to theterminals 4 and 6 of the tube oscillator generator 2. A simplifiedscheme is shown in Fig. 4 which also shows an embodiment in which thepower-transfer devices of the various power-transfer means areinterlocked for the case of two alternately operated work-receivingholes of an induction heating arrangement, so that both power-transfermeans cannot be simultaneously immersed in the work-receiving holes ofthe two coil-units.

-With reference to Fig. 4, ordinary commercial power lines arerepresented at I02 and I04. A switch- I05 is indicative of one or moreprotective or other controls such as an operator-operated foot pedal.Relay contacts I08 are arranged to control the primary energizing powerso that the tube-oscillator generator 2 will not be energized unless apower-transfer means has its power-transfer device immersed in theassociated work-receiving hole of the associated induction-heating coilunit.

A pair of coil-units are indicated at II 0 and I I2, and they areconnected in a single uninterrupted circuit I I4 that includes the powersupply conductors I0 and I2 extending from a tube-oscillator generator2. A power-transfer device H8 is associated with the induction heatingcoil-unit H0, and a similar power-transfer device I20 is associated withthe induction heating coil-unit II,2. Each of these power transferdevices is eiceaaci 7 connected to the end of a reciprocal piston rodI22 that-passes through a pneumatic cylinder I24 for the power-transferdevice I I8 and I26 for the power-transfer device I20. A mechanicalinterlocking arm or lever I28 is centrally pivoted be tween the twopiston rods and the ends of this lever passes through a space locatedbetween pins I30 and I32 for the power transfer device H8 and pins I34and I36 of the power transfer dearms connected to a spanning arm I44which spans the pivot of the lever I28. When the lever pivots so that itapproaches one or the other of its extreme positions, it raises theswitch to close the switch 642. This switch is in an electric circuitI46 having a relay I48 which controls the relay contacts I318. Duringany position of the lever I28 other than its extreme positions, the barI44 drops and opens the switch I42. Consequently, the relay I48 isdeenergized and the main circuit including the power conductors I02 andI04 is open. Consequently, the tube oscillator generator 2 can only beenergized while a power-transfer device is in one of theinductionheating coils and the other power-transfer device is out of theother coil.

It is, of course, to be understood that work is placed in the inductionheating coil that does 1 not have a power-transfer device therein andthe other coil having the power-transfer device therein is innon-working condition.

We have described our invention in simplified embodiments forillustrating the principles thereof. It is obvious that it has wideapplication for power-transfer in connection with high-frequency vcurrents without the use of make-and-break contacts; and that theappended claims should be given their broadest interpretation consistentwith their advance over the prior art.

We claim as our invention:

l. A high-frequency heating system of a type described comprising, incombination, a' single high-frequency supply-means, a pair ofterminal-connections connected thereto, a plurality of high-frequencywork-treating stations each having a highfrequency work-heater andworkholding means'thereat, saidhigh-frequency workheaters" beingaccessible for selective loading and unloading, direct non-switchingconnections from said pair of terminal-connections to said highfrequencywork-heaters, power-selecting means comprising-a plurality of movablemetallic pieces, each piece being associated with a' single oneofwork-treating stations, and support means ope able on saidpower-selecting means for selectively moving said metallic pieces out ofeach respective work station that'is supplied with a workpiece.

2. A high-frequency. system comprising. in combination, a single pair ofhigh frequency supply-conductors, a plurality of high-frequencywork-treating stations, each of said: stations having a high-frequencycoil associated therewith, conductor-means connecting said pair ofsupply conductors-and said plurality of coils in a single commoncircuit, and power-selector means for rendering said coils selectivelyoperable without changing said circuit, said power-selector meanscomprising a plurality of highly conductive metallic pieces, a piecebeing associated only with a single one of said coils, and supportingmeans for movably supporting said metallic pieces for selectivemovement, said supporting means comprising a first means for placing afirst of said metallic pieces inside or outside of a first of said"coils, and a second means for placing a second of said metallic piecesinside or outside of a second of said coils.

3 A system as defined in claim 2 but further characterized by each ofsaid coils comprising an inductionheatin coil, and work-holding meansfor said coils at a side thereof, said supporting means supporting saidmetallic pieces on the opposite side of said coils.

4. A system as defined in claim 2 but further characterized byinterlocking means interlocking. said first and second means so thatsaid first metallic piece is inside said first coil at a time when saidsecond metallic piece is outside said second coil, and vice versa.

5. An induction heating system of a type described comprising, incombination, a plurality of work-treating stations, each work-treatingstation comprising an induction-heatingcoil, a work-holder for each ofsaid induction-heating coils adapted to hold a piece of work ininductiverelation to the associated coil, means for relative-- ly moving'eachwork-holder and its associatedcoil, whereby work on each work-holder isbrought" into and moved out of inductive relation with the associatedcoil, a piece of metal of high conductivity associated with each coil,support means for moving each metal-piece relative to its associatedcoil, whereby each metal-piece is brought intoand out of inductiverelation with the associated coil, and common energizing'means forsimultaneously applying high-frequency energy to said coils, saidsupport means being" operative such that when a workpiece is pos itionedwithin any oneof said coils, the metallic characterized by" supportingmeans supporting said coils so that they are stationary, and means forreciprocating said work-holders and said metal-pieces.

81 A system as defined. in claim '7' but further characterized byinterlocking means between a. metal-piece associated with a coil of afirst worktreating station and a metal-piece associated" ofwork-treating, stations, each work-treating station comprising; aninduction-heating coil, a work-holder for each of said induction-heatingcoils adaptedto hold a piece of work ininductive relation to theassociated coil, means for relatively moving each work-holder and itsassociated coil, whereby work on each work-holder is brought into andmoved out of inductive relation with the associated coil, a piece ofmetal of high conductivity for each coil, supporting means for saidmetal-pieces permitting each of said metal-pieces to be moved from aposition at its associated coil to a position away from its associatedcoil, the latter support means being operative such that when aworkpiece is positioned within the coil at any one of said work treatingstations, the piece of metal associated with the latter coil is moved toa position away from the last said coil energizing means comprising asingle pair of power-supply conductors and connection-conductorsdirectly connecting said power-supply conductor and coils together in asingle circuit, and supporting means supportin each of said workholdersand its associated coil so as to be relatively reciprocable.

References Cited in the file of this patent UNITED STATES PATENTS

